This invention relates to systems for, and methods of, providing for the transmission and reception of signals through unshielded twisted pairs of wires between a repeater and a plurality of clients. The invention particularly relates to systems for, and methods of, using digital techniques for enhancing the recovery, and the quality of such recovery, of the analog signals passing through the unshielded twisted pairs of wires to the client so that the information represented by such analog signals will be accurately recovered at the client.
In a hub-and-spoke network topology, a repeater resides on a hub. The repeater facilitates an exchange of data packets among a number of clients. A client can be a computer, a facsimile machine, another computer, etc. The repeater serves several ports where each port is connected to an individual one of the clients with a separate point-to-point link between the repeater and such client.
In a 100BASE-TX signalling protocol, unshielded twisted pairs of wires constitute the point-to-point link between the repeater and each of the clients. Each link consists of two pairs of unshielded twisted wires. One pair of the unshielded twisted wires provides for a transmission of data from the repeater to an individual one of the clients. The other pair of the unshielded twisted wires provides for a transmission of data from the individual one of the clients to the repeater.
When information is illustratively transmitted from the repeater to an individual one of the clients in a 100BASE-TX system, the information is originally in digital form. The digital information may represent individual ones of a plurality of analog levels. Specifically, in a 100BASE-TX System, the digital signals may represent analog levels of +1, 0 and xe2x88x921.
The digital information at the repeater may be converted to analog form and then transmitted in analog form through the unshielded twisted pair of wires to the individual one of the clients. The transmitted signals are received in analog form at the individual one of the clients. The received signals are then processed to recover the transmitted information represented by the analog information.
The distance between the repeater and the individual one of the clients may be as great as one hundred meters. The unshielded twisted pair of wires coupling the repeater and the individual one of the clients produces a degradation in the characteristics of the signals as the signals pass through the unshielded twisted pair of wires. The amount of the degradation rapidly increases with increases in the length of the unshielded twisted pair of wires connected between the repeater and the individual one of the clients.
The degradation results in part from Inter Symbol Interference (ISI), signal attenuation, crosstalk, clock jitter and a number of other factors. Such degradation severely distorts the transmitted data signals. The degradation also results in part from the fact that the analog information transmitted from the repeater to the individual one of the clients is also received at the other clients connected to the repeater and is reflected back to the repeater, thereby affecting the characteristics of the signals transmitted from the repeater to the individual one of the clients.
Analog techniques have been used in the prior art to process the analog signals received at the individual one of the clients. These analog techniques have not been completely effective in eliminating the degradation or distortions in the signals received at the individual one of the clients. This has caused errors to be produced in the information received and processed at the individual one of the clients. This has been true even though the 100BASE-TX system provides substantially greater noise immunity than other types of systems and is able to handle smaller signal levels than other types of systems.
This invention relates to a system for, and method of, converting analog signals received at a client from a repeater to corresponding digital signals. The digital signals are processed to shift the times for the production of the digital signals so that the digital signals are produced at the zero crossings of clock signals having a particular frequency. The digital signals are also processed to determine at each instant the magnitude of the digital signals closest to the magnitude representing individual ones of a plurality of amplitude levels such as +1, 0 and xe2x88x921 and to then convert such magnitude to such closest one of such amplitude levels. In this way, the information represented by the transmitted signals is accurately recovered at the client.
In one embodiment of the invention, digital signals provided by a repeater connected as by unshielded twisted pairs of wires to a plurality of clients are converted to analog signals. The analog signals become degraded during transmission through the wires. At the client, the degraded analog signals are converted to digital signals. Initially, the phases of the digital signals are coarsely adjusted to have the times assumed for a zero crossing of the digital signals coincide in time with the zero crossing of a clock signal. This phase adjustment is made by determining the polarity, and the polarity of any change, in the digital signals at the time assumed to be the zero crossings of the digital signal.
Subsequently the pre-cursor and post-cursor responses (resulting from the signal degradations) in the digital signals are respectively inhibited by a feed forward equalizer and a decision feedback equalizer. A high pass filter and a tail canceller also inhibit the post-cursor response of the digital signals by limiting the time duration of the post-cursor response.
Phase adjustments are made in the resultant digital signals, after the inhibition in the pre-cursor and post-cursor responses, by determining the polarity, and the polarity of any change, in the digital signals at the times assumed to be the zero crossings of the digital signals. However, before any phase adjustments are made, a phase offset is provided in the digital signals to compensate for phase degradations produced in the signals passing through the unshielded twisted pairs of wires.
Although the invention is discussed in this application with reference to the 100BASE-TX system, it will be appreciated that the invention is not limited to the 100BASE-TX system. For example, the invention is applicable to any 100BASE-TX system. The invention is also applicable to other systems.